In an electronic endoscope described in Patent Document 1, an insert part of a small diameter is inserted into a hole or an abdominal cavity so that an objective lens attached at the tip of the insert part is directed to a diseased part or the like in the direction of insertion. Then, in this state, image information is acquired.
Further, in an electronic endoscope described in Patent Document 2, an objective lens is provided in a side surface of the tip part of an insert part. Thus, an image is acquired within the field of view extending sideward.
Further, in an electronic endoscope described in Patent Document 3, an omnidirectional light receiving unit is provided at the tip of an insert part so that an image covering the entire circumferential directions at the tip of the insert part is acquired using reflection by a convex mirror provided inside the omnidirectional light receiving unit.
Further, an electronic endoscope described in Patent Document 4 is of capsule type used for medical checkup of the alimentary canal in the medical field. This electronic endoscope has an imaging device in the inside, and hence continuously performs image pick-up of the inside of the alimentary canal in the course that the electronic endoscope is conveyed along the inside of the alimentary canal in association with peristaltic motion of the alimentary canal.
In many cases, the imaging device accommodated in the tip part of such an electronic endoscope has a smaller area and a smaller number of pixels than a solid-state imaging device used in a digital camera or the like. Thus, when a detailed image of a diseased part or the like is acquired, the image information obtained by each single image pick-up is limited to the image of a small view field region.
Thus, when detailed image information is to be acquired over a large region, the operator of the electronic endoscope need repeat image pick-up multiple times with adjusting the insertion position of the electronic endoscope by manual operation. Thus, attention need be paid to both of the operation of searching a diseased part or the like, that is, adjusting the insertion position, and the operation of image taking. Thus, skill has been necessary in such work.
Further, in the electronic endoscope in which an image over the entire circumference of the tip of the insert part is acquired using an omnidirectional light receiving unit, image information over the entire circumference region of the insertion position where image pick-up is performed is obtained at once. Nevertheless, the image pick-up region is restricted to a region of a narrow width at the insertion position. Thus, in order that entire circumferential image information should be acquired over a large region, image pick-up need be repeated in such a manner that the insertion position is adjusted at each time. This causes a possibility that information is missing at a junction part of images or that useless image pick-up is repeated.
Further, the electronic endoscope of capsule type is conveyed along the inside of an alimentary canal by peristaltic motion of the alimentary canal. Thus, the operation of moving the field of view is unnecessary. Nevertheless, such an electronic endoscope is not applicable to a hole or an abdominal cavity where peristaltic motion is absent.